I have full planning for a 4 bed house which was given June 08 and is due to start by June 10. I have been told that I must get the project started by that date or lose my planning and that I should aim to get the build up to ground level. I am uncertain as to whether I want to sell or keep with the current financial situation. What costs would be involved if I have to get the build to ground level and would a buyer be put off by this.

If you have planning you have plans. Ask your architect and / or your builder.

I'm afraid noone on here will have the slightest idea as to your incurred costs and guessing would be madness. Nor is it likely that anyone is in a position to fortell a potential buyers reaction. Sorry.